For marketing and other reasons, manufacturers of radio communications devices typically offer several different configurations for each communications product manufactured. A particular model of mobile radio transceiver may have a "basic" or minimal configuration but may optionally be provided with additional features or "options" at additional cost.
For example, a basic transceiver configuration may provide communications over a limited number of communications channels for basic radio transmitting and receiving functions required by all users. Some users may, however, have additional requirements requiring additional features--such as additional communications channels, receiver channel scanning, public address capability, and tone activated squelch. The ability of a manufacturer to provide such additional "options" permits increases in the flexibility, versatility, desirability and range of applications of the product without penalizing purchasers of the basic configuration with increased cost. Purchasers of the basic model pay a minimum price for the minimal configuration, while users requiring additional "option" features pay an increased price based on the number and type of options required.
In the past, additional options were generally provided by incorporating additional components and circuitry into the device. For example, in the past channel scanning capability or additional operating channels were added by installing additional frequency selection circuitry into the transceiver. Similarly, the tone activated squelch option typically required an additional tone decoder circuit to be installed. Transceiver designers used modular architectures to accommodate additional plug-in "option modules."
An example of this design approach is the prior art "MLS" series radio transceivers manufactured for General Electric Company by Japan Radio Corp. These "MLS" transceivers include basic transceiver circuitry disposed within a housing. The front panel assembly of the transceiver housing was manufactured separately, and consists of a separable front panel "escutcheon" plate. Mechanically mounted to the escutcheon plate is a printed circuit board which plug-connects to the basic transceiver circuitry when the escutcheon plate is mechanically fastened to the housing. The escutcheon plate and associated printed circuit board comprises a module separable from the transceiver main housing and basic circuitry. The module includes user controls mounted on the escutcheon plate and circuitry required to connect user controls mounted on the plate to the transceiver circuitry.
Since different "option" features in many cases require different additional user controls, different models of escutcheon plate modules were produced for the "MLS" series transceivers. In particular, the "MLS" transceiver was made available in five different versions: (1) a two-channel "basic" version; (2) an 8-channel version with the scan feature; (3) a 16-channel version without scan; and (4) a 16-channel version with scan feature. Five different interchangeable escutcheon plates with different user control arrangements corresponding to these five different transceiver versions were also made. The particular escutcheon plate/control panel installed on a particular "MLS" transceiver limited the transceiver features the user could access. For example, the escutcheon plate corresponding to the "MLS" transceiver version with 16-channel capability and no scan feature does not have a control to actuate the scan feature--preventing the user from obtaining the benefit of the scan feature. Similarly, the escutcheon plates corresponding to the 8-channel transceiver versions do not include user controls to access more than 8 channels.
Since all "MLS" transceivers included identical basic transceiver circuitry and main housing, reduced manufacturing costs and increased reliability derived from large scale manufacturing were obtained. Specific purchaser selected options could be provided in a particular unit simply by installing the appropriate escutcheon plate module--a procedure which could be performed in the field if desired. Incorporation of the circuitry performing the option functions and user controls interacting with such circuitry within the same front panel escutcheon plate module permitted a transceiver to be reconfigured by simply "unplugging" one module and "plugging in" a different module (further increasing reliability and decreasing manufacturing costs).
Digital microprocessor controlled radio communications devices such as the "MLS" series transceiver are generally known, of course. The following (by no means exhaustive) listing of prior issued patents is generally relevant to the state of the art of so-called "digital radios":
U.S. Pat. No. 4,378,551--Drapac PA1 U.S. Pat. No. 4,392,135--Ohyagi PA1 U.S. Pat. No. 4,525,865--Mears PA1 U.S. Pat. No. 4,247,951--Hattori et al PA1 U.S. Pat. No. 4,254,504--Lewis et al PA1 U.S. Pat. No. 4,510,623--Bonneau et al PA1 U.S. Pat. No. 4,688,261--Killoway et al PA1 U.S. Pat. No. 4,618,997--Imazeki et al
Such references teach controlling transceiver functions in addition to transceiver operating parameters (e.g., operating frequencies) in response to digital signals stored in a memory device.
While older radio transceivers required additional circuitry to perform additional, optional functions such as channel scanning, tone activated squelch and the like, modern digital microprocessor controlled transceivers are capable of performing such additional functions under software control with little or no additional circuitry. For example, receiver channel scanning can be implemented by providing an enhanced receiver program control routine which controls the microprocessor to periodically monitor activity on various channels--and additional frequency data can be stored in a memory device to provide additional transceiver operating channels. Additional tone decoding and control algorithms performed by the microprocessor under control of additional program control software can provide advanced squelch control functions, tone signalling functions, and the like.
It would be unfair (and also poor marketing strategy) to make users needing only a minimal transceiver configuration pay for the high development cost of advanced option features and enhancements. Accordingly, for various reasons it is still very much advantageous to offer the purchaser a "basic" lower cost transceiver configuration while permitting him to select additional option features at higher cost--even though the main (or only) difference between the basic and option configured transceivers may reside in the specific program control routines they respectively execute. This marketing strategy allows the manufacturer to offer the basic unit at reduced cost and at the same time requires purchasers requiring enhanced operation to bear the additional costs associated with developing and providing the additional option features. For this marketing strategy to be successful, however, purchasers of low cost basic transceiver configurations must not be able to easily modify their units to obtain more expensive option features.
One possible way to obtain this result is to provide different transceiver configurations, each configuration including a different PROM (programmable read only memory) storing only the subset of the program control instructions and transceiver parameter data associated with that specific configuration. This approach has several disadvantages, however. One important disadvantage is that field "upgrading" of a transceiver is very difficult and time consuming, since the transceiver has to be disassembled, the old PROM removed, and a different PROM installed.
Commonly assigned U.S. Pat. No. 4,525,865 to Mears discloses an arrangement whereby a non-volatile memory within a mobile radio transceiver can be reprogrammed without physical entry or removal of components to provide the radio with additional operational options (e.g., tone or digital addresses, carrier control timers, or the like).
U.S. Pat. No. 4,392,135 to Ohyagi and U.S. Pat. No. 4,378,551 to Drapac disclose security arrangements for enabling and/or inhibiting option features in paging receivers.
Ohyagi teaches an "information setter circuit" comprising an 8.times.9 bit PROM in which is stored "option selection bits" for selecting various functional options of the paging receiver (e.g., automatic resetting after an alert, paging by mechanical vibration in lieu of tone, and a battery saving feature). The microprocessor reads the information stored in this circuit as an input to the program control algorithm it executes and enables or inhibits the various option features accordingly.
The Drapac patent discloses discrete logic security circuitry incorporated as part of the pager which connects with option selection circuitry contained in a separable "code plug." The code plug includes circuitry which controls tone decoding, and additional simple fusible link type circuitry which controls selection of various options such as battery saving, automatic reset, and dual call operation. Logic level signals are connected through the fusible links in the code plug to the security logic circuitry, and the logic circuitry in turn enables or disables the various options. The security logic circuitry detects when a user tampers with the code plug fusible link connections and prevents activation of the paging device whenever tampering occurs.
While such arrangements may be satisfactory in the context of a paging device, they do not readily lend themselves to the more complex environment of a full-feature digital radio transceiver--in which many more options may be provided and some additional circuitry and user controls may be required to implement the various options. In addition, greater security than Drapac's code plug can provide is necessary to prevent purchasers from successfully enabling transceiver advanced option features through tampering.
The present invention, like the prior art "MLS" series radio transceivers described above, provides different transceiver front panel escutcheon plate modules for different optional transceiver configurations. Unlike the prior art arrangement, however, the present invention does not rely merely on the absence of certain user controls to prevent a user from accessing and operating "option" features of the transceiver. In accordance with the present invention, a security circuit is provided in the module in addition to user controls and associated control circuitry. The security circuit is connected to communicate serial data signals to and from a digital signal controller (e.g., microprocessor) which is part of the main transceiver circuitry. In the preferred embodiment, the security circuit is a single chip programmable logic array which implements certain Boolean logic equations, the specific equations corresponding to a specific option configuration.
The transceiver controller is capable of performing any of various basic and option functions under control of program control instructions stored in a non-volatile memory also part of the main transceiver circuitry. The transceiver controller causes the security circuit to generate a data byte in response to signals provided by the controller, and enables and disables transceiver "options" in response to the value of the generated data byte.
In particular, upon initial application of power to the transceiver, the controller transmits a sequence of digital signals to the security circuit. The security circuit permutes the sequence of signals into a different sequence, the specific permutation used being of arbitrary complexity--and dependent on transceiver "option" features to be enabled. The security circuit communicates the permuted signal sequence in serial form back to the controller. The controller enables (executes) portions of the program control instructions stored in its associated non-volatile memory and disables (does not execute) other portions of the stored program control instructions in response to the sequence received from the security circuit.
The protection against tampering provided by the present invention is far greater than that provided by any of the prior art arrangements described above. This is in part because the security circuit must respond to a serial data sequence which is fleeting and in part because the permutation of that data sequence performed by the security circuit can be an arbitrarily complex function. Far more than mere grounding of pins of a connector or the like would be required to defeat the security circuit and its interaction with the controller. Exact copying of the security circuit might be necessary to duplicate the functionality of the circuit in a form sufficiently miniaturized to be physically disposed on an escutcheon plate.